Recent investigations have suggested that sepsis associated tissue injury may occur in large part as a result of the effects of endotoxin upon circulating phagocytes and vascular endothelium. Current concepts suggest that the endotoxin effects may be mediated by the monokines, interleukin 1 (IL-1) and tumor necrosis factor (TNF). This application proposes to study this concept from multiple perspectives. First, patients with sepsis and sepsis- induced adult respiratory distress syndrome (ARDS) and controls will be evaluated for evidence of IL-1/TNF activation in their biological fluids and mononuclear phagocytes using state of the art antigenic enzyme linked immunoassays and mRNA analysis. Second, factors that control monokine production and release will be evaluated. These studies will include a characterization of the heterogeneity in endotoxin responsiveness in humans as measured by endotoxin receptor density and by responsiveness for monokine production. They will also study IL-1 regulation in a naturally occurring model of monokine regulation, i.e., the inherent differences between blood monocytes and alveolar macrophages in monokine release. In addition, factors that inhibit monokine action will be evaluated in detail. This evaluation will include the characterization of natural occurring monokine inhibitors that may represent protein modulators of monokine action and hence potent modulators of the development of sepsis-induced tissue injury. Finally, sensitive mRNA probes will be used to analyze human and animal tissue for the evidence of in vivo activation of IL-1/TNF genes. In particular, an animal model of sepsis will be studied with in situ hybridization localize the origin of monokine production. Taken together these studies should not only clarify the cellular mechanisms that may predispose to sepsis-induced injury such as ARDS, but also delineate new ways to modify and/or prevent the devastating consequences that result from endotoxemia.